Energetic cost of protein turnover in healthy elderly humans

OBJECTIVE: Whole body protein turnover (PTO) and resting energy expenditure (REE) are both correlated to fat-free mass (FFM), in young and elderly sub jects, and REE is positively correlated to PTO in young adults. Thus, the a im of this study was to compare the energetic cost of PTO in young (n = 39, 23.4 +/- 3.1 y) and elderly (n = 41, 67.5 +/- 3.6y) healthy volunteers. MEASUREMENTS: REE (indirect calorimetry), PTO (C-13-leucine isotopic diluti on) and body composition (bioelectrical impedance analysis with age-specifi c equations) were measured in the postabsorptive state. RESULTS: Elderly subjects had a higher fatness (30.5 +/-7.1 vs 18.2 +/-5.5% , elderly vs young, P <0.001), a similar REE (0.97 +/- 0.13 vs 1.06 +/- 0.1 5 kcal min(-1)), and a lower PTO (1.28 +/- 0.22 vs 1.44 +/- 0.18 mu mol kg (-1) min(-1), P < 0.001). PTO, REE and FFM were significantly correlated an d after adjustment for FFM, REE was positively correlated to PTO (r = 0.61, P < 0.001). The slope of this relationship was the same in both groups, wh ile the adjusted mean REE was lower in elderly subjects (0.97 +/- 0.09 vs 1 .05 +/- 0.07 kcal min(-1) , P < 0.01). CONCLUSION: In comparison with young subjects, the energetic cost associate d with PTO in elderly subjects is not different, but the proportion of REE not associated with PTO is lower.